Which type of photodetector employs a linear arrangement that allows it to respond to a specific wavelength resulting in complete UV/visible spectrum analysis?

• A. Photomultiplier tube
• B. Phototube
• C. Barrier layer cell
• D. Photodiode array

Answer: (D)

The key idea is detecting an entire UV/visible spectrum in one shot by using a detector that has many sensing elements lined up in a row. A photodiode array is exactly that: a linear arrangement of many photodiodes, with each diode acting as a separate channel. When light is dispersed by a grating or prism, or when the diodes are arranged to correspond to different wavelengths, each element responds to a different portion of the spectrum. This lets the instrument capture the full spectrum simultaneously, giving complete UV/visible spectrum analysis quickly and with good spectral resolution.

Other detectors are single-channel devices. A photomultiplier tube or a phototube provide very high sensitivity but measure one wavelength (or require moving a monochromator to scan wavelengths) at a time. A barrier layer cell detects light in a limited range and isn’t arranged as a linear array for simultaneous multi-wavelength detection. So, the photodiode array uniquely provides the linear, multi-channel capability needed for full-spectrum analysis in one measurement.